In recent years wireless and RF technology have dramatically changed our perceptions, use, and reliance upon portable electronic devices. The uses of wireless technology are widespread, increasing, and include but are not limited to telephony, Internet e-mail, Internet web browsers, global positioning, photography, diary, address book, and in-store navigation. Additionally, devices incorporating wireless technology have expanded to include not only cellular telephones, but Personal Data Analyzers (PDAs), laptop computers, palmtop computers, gaming consoles, printers, telephone headsets, portable music players, point of sale terminals, global positioning systems, inventory control systems, and even vending machines. Today many of these devices are high volume consumer commodities where both carriers and portable electronic device manufacturers compete for the users' money through features, network coverage, signal strength and clarity (bit error rate) while reinforcing customers desires for small and lightweight devices, long battery life, increased roaming, guaranteed connectivity and increased digital download speeds.
Amongst the multiple standards and technologies, Orthogonal Frequency-Division Multiplexing (OFDM), has reached commercial deployment and success through its use within many applications including, but not limited to:                ADSL, SDSL and VDSL broadband access via POTS copper wiring;        Wi-Fi Wireless Local Area Networks, according to IEEE 802.11;        WiMAX Wireless Metropolitan Area Networks, according to IEEE 802.16;        Mobile Broadband Wireless Access (MBWA) systems, according to IEEE 802.20;        Digital Audio Broadcasting (DAB);        Digital Video Broadcasting for terrestrial digital TV (DVB-T);        Fast Low-latency Access with Seamless Handoff (FLASH) cellular infrastructure for packet-switched cellular networks;        Power line communications (PLC) for providing home networking on residential electrical power cabling; and        Multimedia over Coax Alliance (MoCA) for home networking over in-home coaxial cable.        
Many of these OFDM portable electronic devices are mobile, as they are associated with users performing tasks as they move, and in many instances the users will be highly mobile as they use these electronic devices in their personal vehicles, or in public transportation such as buses, taxis and trains. For such OFDM systems these high mobility environments provide significant challenges to the system designers in two different aspects. On the one hand, due to the Doppler induced Inter-Carrier Interference (ICI), an accurate estimation of the Channel Frequency Response (CFR) at each sub-carrier is difficult to obtain. On the other hand, in fast fading environments, even with perfect CFR estimation, ICI likely causes severe degradation of the system performance. These factors result in incorrect determination of received symbols, thereby providing degraded signal quality to the user.
For fast fading channels, various channel estimation techniques have been developed based on the availability of time or frequency-domain pilots.
For channel estimation with time-domain pilots, an entire OFDM symbol is normally inserted periodically as pilot symbol. In order to maintain the performance, the space between two adjacent pilot symbols is less than 1=(2·fd·Ts) symbols, where fd·Ts is the normalized fading rate, fd is the maximum Doppler spread and Ts is the useful OFDM symbol duration. Therefore, the system throughput decreases quickly with increase of the fading rate due to the increased pilot symbol rate.
To reduce such throughput loss, pilot symbols with shorter duration than the OFDM symbol have been used. Nevertheless, for the systems with only frequency domain pilots, where a subset of sub-carriers is dedicated as pilot sub-carriers, e.g. DVB-T, frequency-domain pilot-aided channel estimation is the only choice. It has been shown that time-varying channels also provide time diversity that has been exploited to improve the error performance. However, exploiting time diversity strongly hinges on accurate estimation of the channel matrix, including both the effects of channel gain, which is defined as the channel frequency response at the kth sub-carrier, and ICI gains, which represent the multiplicative gains applied to the neighbor sub-carriers.
It would be advantageous to provide receivers with a simple process for estimating channel gain and ICI interference of fast fading channels.